python 元组推导式

>>> b=(page for page in range(10))
>>> print(b)
<generator object <genexpr> at 0x0000000002EE61C8>
>>> list(b)   #只能生成一次
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> list(b)
[]
>>>